The present invention relates generally to wastewater treatment systems and relates more particularly to a novel overland flow type treatment system.
The overland flow treatment of wastewater involves the application of the wastewater to a sloping terrace of impervious or relatively impervious soil which is planted in a grass crop compatible with heavy irrigation. The wastewater flows in a thin film over the surface of the terrace and becomes purified upon flowing slowly through the grasses and the soil surface by biodegradation of the organic impurities by the soil microorganisms and/or chemical-mechanical removal of inorganics by the soil complex. Since the soil is impervious or relatively impervious, a large percentage of the wastewater is collected as runoff in substantially purified form with the remainder being absorbed into the soil, consumed by the plant life, or evaporated into the atmosphere. The overland treatment is particularly well adapted for the disposal of food processing wastewater containing large amounts of organic materials or other similar types of wastewaters including most municipal sewage wastewaters. The employment of overland flow systems has been pioneered by Campbell Soup Company plants, including those having heavy seasonal wastewater flows such as tomato processing plants.
The overland flow treatment is conventionally carried out utilizing natural hill sites, although in most cases, the sites are modified to produce a satisfactorily uniform slope of between 2% and 8% and a smooth surface to prevent the channeling of the water flow. The wastewater is applied to the hillside in a conventional overland irrigation system by fixed conduits or laterals which typically comprise pipes lying on the surface or below the surface of the slope and having rotating sprinkler heads located at intervals along the conduits or laterals and arranged to spray the wastewater predominantly on the upper regions of each slope. The wastewater is permitted to flow along the slope surface for a distance of approximately 175-250 feet and is then collected by suitable drains and either recycled or directed into a local stream or river.
The conventional overland flow system as briefly described has been extremely successful and the present invention utilizes the proven overland flow principles including the distribution of the wastewater to carefully graded slopes, the passage of the wastewater across the grass covered slope surfaces and the collection of the purified water at the bottom of the slopes. The present invention differs primarily in the manner in which the slopes are formed and the manner in which the wastewater is distributed to the slopes.
The overland flow system although economical to operate can be initially quite expensive to develop, primarily because of the work required to reform the natural contours of the earth in the selected area and the high cost of installing the fixed wastewater distribution system. The slopes must be uniformly graded to prevent puddling, channeling and erosion and to provide the desired retention time of the water. With natural slopes, it may not be possible to use all of the available land due to natural terrain irregularities. Although tiers of terraces can in some cases be provided on an appropriately sloping hillside, the more usual situation is a single flow area on a given hillside utilizing the optimally sloping portion to receive the wastewater flow.